1. Field of the Invention
The present invention relates to a light-beam scanning type image reader, and more particularly to an improvement in the method of adjusting lengths across which a scan body is scanned or read.
2. Description of the Related Art
A light-beam scanning type image reader is known in which an image signal is obtained by scanning a light beam on a scan body recorded with an image and photoelectrically reading luminescent light emitted according to the recorded image.
As the light-beam scanning type image reader, a radiation image recording-reproducing system and an autoradiographic system have been proposed and already been put to practical use by the applicant of this application. These systems take advantage of the photostimulated luminescence (PSL) of a storage-type phosphor (stimulatable phosphor) in which the phosphor is irradiated with radiation (X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, electron rays, ultraviolet rays, etc.) and emits luminescent light according to the stored radiation energy when irradiated with excitation light such as visible light, etc. That is, by irradiating a radiation image, transmitted through a human body, etc., to a storage-type fluorescent sheet, or by exposing the tissue of a living organism, containing a drug labeled with a radioactive substance, to direct contact with the storage-type fluorescent sheet only for a predetermined time, the radiation image, such as the transmitted radiation image, the directly exposed image, etc., is temporarily stored and recorded on the storage-type fluorescent sheet. Then, excitation light, such as laser light, etc., is scanned on the storage-type fluorescent sheet to obtain photostimulated fluorescent light according to the radiation image, stored and recorded on the sheet. The obtained photostimulated fluorescent light is converted to an electrical image signal. Based on the image signal, the radiation image is output as a visible image to a recording material such as a photosensitive material, etc., or to a cathode-ray tube (CRT) display unit, etc.
In these light-beam scanning type readers, a light beam, reflected and deflected by a rotating polygon mirror, is scanned on a scan body in a horizontal scanning direction, and at least either the light beam or the scan body is scanned in a vertical scanning direction approximately perpendicular to the horizontal scanning direction. Through a combination of the horizontal scan and the vertical scan, the light beam is uniformly scanned on the scan body.
In the case where an image signal is read out from a scan body by the above-mentioned image reader, incidentally, image signals must be obtained at a fixed number of pixels from a scan body, if the scan body has a fixed form.
However, there are cases where fabricated image readers have a different number of pixels because of the cumulation of allowable fabrication errors, etc., of each component of the optical system, electrical system, mechanical system, etc., which constitute the image reader. Because of this, image signals cannot be always obtained at a fixed number of pixels from a fixed form of scan body. In addition, there are instances where a desired number of pixels vary with each user of the image reader. Thus, it is desired that these cases are flexibly handled.